Modem manufacturing practices often require machinery including linear actuators, for cutting, forming, punching, and/or joining together components formed from raw materials in a variety of forms, such as sheets, bar stock, billets, or pellet. Such machinery is often required to apply substantial compression loads, of, for example, 75 to 100 tons, and be capable of rapid cycle times, to promote efficient, effective, low cost production.
High capacity machinery, of the type used in cutting and forming motor vehicle body panels and the like, for example, typically have first and second structures in the form of upper and lower platens, each carrying part of a die set. The upper platen and upper die are typically driven vertically in a reciprocating motion by a drive mechanism including some form of linear actuator. The lower platen and lower die are generally stationary, but in some widely used types of metal forming machinery, a die cushion mechanism may be provided, adjacent the lower platen, for clamping an outer perimeter of a sheet of material being formed by the die set. Such die cushion mechanisms may also include a plurality of linear actuators for maintaining the clamping pressure on the edges of the work piece, as the work piece moves vertically during formation by the die set.
In the past, linear actuators of the type used in material forming machinery were primarily hydraulic and/or pneumatic actuators. Hydraulic and/or pneumatic actuators are typically capable of producing high operating forces at reasonably high cycle rates over a relatively long operating life of the machine. Hydraulic and/or pneumatic actuators are sometimes rather large in physical size, however, and require auxiliary equipment, such as pumps, valves, fluid tanks, and fluid cooling devices, which also are rather large in physical size. Hydraulic actuators often require considerable maintenance, and are prone to leakage over the operational life of the machine. Pneumatic actuators typically are incapable of being controlled, to the degree required for modern die press operations.
As material forming methods have become more sophisticated, mechanically driven actuators, having mechanisms such as ball screws, roller screws, or rack-and-pinion arrangements, for example, have begun to supplant traditional hydraulic actuators. Such mechanical actuators are typically smaller in physical size, than a corresponding hydraulic actuator, and may be capable of more rapid response and have greater controllability than hydraulic actuators. Mechanical actuators also eliminate the problem of fluid leakage inherent in the use of hydraulic actuators. U.S. Patent publications disclosing mechanical actuators for use in material forming machinery include: U.S. Pat. No. 5,522,713, to Lian; U.S. Pat. No. 5,435,166, to Sunada; U.S. Pat. No. 6,640,601 B2, to Hatty; U.S. Pat. No 5,656,903, to Shui, et al.; and US 2006/0090656 A1, to Iwashita, et al.
In a sophisticated die cushion apparatus, for example, a plurality of linear actuators may be closely positioned to one another around the perimeter of the workpiece. As the workpiece is formed, the clamping pressure applied by individual ones of the linear actuators may be varied, by a numerical control apparatus for example, to allow movement of material in selected sections of the periphery to preclude tearing or wrinkling of the workpiece during the forming process. To allow for such close positioning of the linear actuators, the individual actuators must be small in physical size. It is also desirable, that if one of the plurality of linear actuators should need to be repaired or replaced, that the individual linear actuators be modular in nature to facilitate removal and replacement of the defective actuator so that production on the material forming machine having the die cushion may be resumed as quickly as possible. It would be desirable to use mechanical actuators in such applications, rather than hydraulic actuators, due to the smaller size and more inherently modular construction of mechanical actuators, compared to hydraulic actuators.
Despite their significant inherent advantages, in a number of respects, over hydraulic actuators, the use of mechanical actuators in material forming machinery has been limited to date, due to wear and fatigue failure of the mechanical components of the mechanical actuator resulting from the large forces and cyclical loading on the mechanical components, inherent with the use of linear actuators in material forming machinery.
It is desirable, therefore, to provide improved apparatuses and methods for utilizing mechanically driven linear actuators in material forming machinery, in a manner which overcomes the problems addressed above. It is also desirable to provide such improved apparatuses and methods in a form which may be readily adapted for use as a primary linear actuator, in a platen press or a metal cutting shear, for example, and in applications, such as a die cushion mechanism, having a plurality of linear actuators performing a secondary clamping function in conjunction with one or more primary linear actuators providing a primary force for a material forming operation. It is further desirable, that such an improved apparatus and method also be in a form which is readily controllable and/or reconfigurable so that a given material forming machine may be conveniently used for a variety of operations, and/or with die sets, for example, of varying sizes and weights.